Lift trucks, material handling and industrial vehicles, and other types of vehicles are frequently constructed using electric motors. To power these vehicles, electric storage batteries, typically lead-acid batteries, are used. These batteries are typically sized to provide sufficient charge for a work shift or other defined period, so that the vehicle remains sufficiently charged during the entire work shift, and can be recharged when the shift is complete.
It is desirable, however, to extend the useful charge life of the battery between off-duty charging cycles. To meet this need a number of different systems have been developed. One method for extending the charge of the battery is known as opportunity charging. In opportunity charging, the truck is plugged into a charger during breaks or other non-work periods, to allow for recharging of the battery. This method is helpful in increasing the efficiency of the vehicle, but requires the installation of high kilowatt electrical service throughout a facility, which is both expensive and space-intensive. Moreover, opportunity charging returns only between about five and ten percent of battery charge during an operator break, thereby providing a relatively low return on a significant investment. Additionally, the charging is relatively slow, requiring the vehicle to sit for a significant period of time.
Another method for extending the life of a battery during use is known as fast charging. In fast charging, a large battery charger that operates at two to three times the output of the current as a regular battery charger is used. These devices can deliver, for example, four hundred to six hundred amperes during work breaks, and therefore deliver a significantly higher amount of energy to the battery in a reduced time as compared to regular chargers. Fast charging, however, requires alteration to the vehicle to permit the use of special connectors installed on the battery. As with opportunity charging, significant and expensive alterations must be made to the facility to enable charging. Furthermore, the concentrated application of charge to the battery results in significant heating of the battery, and the elevated temperature can be detrimental to the life of the battery.
There remains a need, therefore, for an inexpensive, and efficient method for maintaining the charge on a battery during use. The present invention addresses these issues.